Method of bonding a filter paper tube to supporting end plates



3 14 5 QM we? Q wig. pm 52 F P Feb. 23, 1965 J. A. NORTON ETAL METHOD OFBONDING A FILTER PAPER TUBE TO SUPPORTING END PLATES IMPREGNATE PAPERWITH THERMOSETTING RESIN HEAT-JMPREGNATED PAPER TO REMOVE SOLVENT FOLDPAPER IN FORM OF BELLOWS APPLY VINYL PLASTISOL ADHESIVE TO END PLATESAND ASSEMBLE FILTER Filed May 4. 1961 IN VEN TORS ATT RNEY United StatesPatent 3 170 826 METHOD or noNnnJo h rirrnn PAPER roan TO SUPPQRTHNG ENDPLATES James A. Norton and David P. Lake, Flint, Mich, assignors toGeneral Motors Corporation, Detroit, Mich, a corporation of Delaware JFiled May 4, 1951, Ser. No. 107,705

6 Claims. (Cl. 156-69) ing surface area and structural strength, towhich is fastened on each end thereof an end plate of relatively rigid.material such as metal or a fiber reinforced plastic material.Perforated metal sheels disposed along the length of the paper cylinderprovide the element wtih structural strength. The filter elements areinserted into a housing whereby the fluid to be filtered passes into thefilter radially of the paper element and passes out through the axialopening thereof; The end caps and side shells provide means forsupporting the filter element within the filter housing. 7

Typical practice in the manufacture of the filter paper involvesfirstimpregnating it with a'suitabl'e heat-curable phenol-formaldehyde resinwhich is capable upon curing of providing the paper with resistanceagainst tearing and collapse without impairing the porosity 'andfiltering;

capability thereof. Desirably the paper is adhesively bonded. to theendplates by means of an adhesive which upon curing will exhibit asufficient' degree of flexibility so that the typical car vibrationswill not fracture the bond between the filter paper and theend plateswhich will cure substantially below the charring temperatures of thefilter paper andwhich willnotgbe attacked by the 3,176,826 Patented Feb.23, 1965 r Ice FIGURE 2 is an end view of the element in partial crosssection; and

FIGURE 3 is a flow diagram of the method ofthis invention.

As shownin FIGURE 1, a paper-type filter element involved in thisinvention includes a folded paper element 10 formed into a cylinderhavinga central axial opening 12 therethrough. To each end .of the papercylinder there is bonded a rigid plate 14 by means for an adhesive layerl6. Preferably the plates 14 include flanged or offset end portions 18and an inner flanged or offset portion 20 which serves to form adepression for retaining the ends of the filter element 10, and an innerperforated shell 15 which provides the assembly with suitable structuralstrength. As will be hereinafter described, the. ad-

hesive layer 16 is deposited in the depression between the offsetportions 18 and 20 of the end plate in liquid form.

The end of the paper element is immersed'in the adhesive layer so thatthe adhesive will soak into the paper element to insure that a sealingbond is formed between the paper and the end plate.

"'As is well known in the art, the filter element as shown in FIGURE 1is clamped in a housing so that a seal is provided between the endplates 14 and the housing. The housing is arranged so that the fluid tobe filtered enters .the central space 12 of the filter in a directionradially of the paper cylinder and passes out through the axial opening12.

In general, the manufacture of the filter element involves thesequential steps of first impregnating'the paper :with a suitablethermosetting resin suspended in a low viscosity solvent, then'subjecting the iIn regnated'paper to heat to drive'off. the solventwithout significantly curing the resin, folding the paper andforming itinto a cylinder as shown in FIGURE 1, applying the adhesive material to.Cthe depressions .formed between the offset portions 18 and 20 in theform of a layer 16, thenrassembling the;

end plates and paper element so that the ends of the paperelement areimmersed in the adhesive layer-lSjand finally the assembly is placed inan oven for a predetermined time whereby the resin impregnant will cureto a petroleum hydrocarbon fluids in connection1with which it is used.

It is the basic object ofthisinvention' tbjaprovide a1 more eflicientand economical method for making papertype filter elements whichinvolves the-use ofa resinous composition for impregnating the filterpaper and; a vinyl plastisol adhesive for bonding the filter paper-tosupport-, ing' end plates which will cureat reduced temperatures in. pthe vicinity ofrabout 300 F. to, 320 'F., a temperature rangesafely-below the chairing temperature of the paper and a temperature atwhichiboth the impregnant and the? adhesivewill efiiciently andeconomicallylcureiri a single heating operation. g

This and other objects plished by providing a process for making filterelements in which the adhesivefor bondingthetfilter paperto'thesupporting'end plates comprises major proportions of a vinylplastisoland minor ,proportions'ofa compound selected from'the group consistingof a phenol having 2 to 4 hydroxyl groups attached to the"benzenef-ringfand an aminophenol, and a material such ashexamethylenetetraminewhich-is nonreactive witharespecbto the polyhydric. I phenol or'aniinophen'ol at room temperatures but which atelevatedtemperatureswill'decompose to generate an 1 aldehyde. 7

Other objects and advantages of the invention will be i apparent fromthe following detaileddescription of ,the

of the invention .are accorn-f invention .made .inconjunction with 'theaccompanying drawing, in which: I

.FIGURE 1 is an elevation view of a filter element;

in partial crosssection predetermineddegree without charring. and theadhesive will cure to firmly bond the paper cylinder 10 to the-endplates.

I The firststep in the manufacture of the filter element involvestheimpregnationof the paper in order to impart toit suitable structuralresistance toward collapse and .7 tearing in operational-use.Preferablvthe paper'fis'im-r pregnated with a resol phenolic varnish bymeanspf a calendering apparatus such as isdisclosedin the United.ljStates Patent No; 2,700,620 Somers, assignedto the.as-'

"signee of the present invention. This=resin"varnish con:

sists. essentially of theiresole formof phenol-formaldehyde resincontainedin a solvent such as ethanol. A"

preferred impregnant for this purpose is, disclosed in the copendingpatent application Serial No. 107,704, filed May 1 4, 1961,.filedsimultaneously herewith andassigned'to the assignee'of the presentinvention. Theimpregnatedpaper, is passediinto a drying oven wheremostlofthe solvent is materialto permit subsequent folding and handlingof the a paper. This oven is preferably maintained at a tempera:

permitted'to evaporate without significant cure of the resin ture ofbetween 1409 F. and 190 F. depending upon the character of theimpregnant used. The resole type. resin which is deposited in thefilter'paper will readily cure at temperatures rangingifrom; about 2?,F. to 360 F However, since the-paper tends to char in the vicinity ofabout 345 F,, it is essential that the curing of the paper impregnant beaccomplished quickly and preferably at temperatures substantially below345 F vision of a vinyl plastiso l adhesive to form the adhesion Animportant aspect of this invention involves the pro.

layer 16. The bond produced by means of the adhesive compositon of thisinvention is at least equal to the strength of the paper, it isrelatively flexible on beingcured and is substantially inert withrespect to petroleum hydrocarbons and may be efficiently cured atreduced temperatures in the vicinity of about 290 F. to 320 F. duringthe same time that the resole base paperv impregnant is cured to between83% and 92% of completion, the desired degree of cure of the impregnant.This curing temperature provides a highly advantageous margin of safetywith respect to the danger of charring of the paper. The bonds producedat these lower temperatures are equivalent to or superior to the bondsproduced by other vinyl plastisoltype adhesives at higher temperatures.

In general, the term plastisol as used herein is intended to refer to aliquid material comprising a finely divided solid vinyl resin such aspolyvinyl chloride suspended in an organic liquid which has aninsignificant solvent efiect on the resin at room temperature but whichat elevated temperatures solvates the solid resin to gel and fuse toform a material resembling a cured rubber. In the preparation of atypical plastisol a vinyl resin such as polyvinyl chloride or acopolymer of vinyl chloride and other vinyl resins such as vinyl acetateand vinylidene chloride is thoroughly dispersed in the organic liquidwhich is generally termed a plasticizer. Typically, the resin is arelatively high molecular weight ester or a mixture of esters such astricresyl phosphate, dioctyl phthalate, dibutyl sebacate and the like.Other plasticizers commonly used include polymeric polyesters andepoxidized vegetable oils. To this dispersion there may be addedstabilizers such as dibasic lead phosphate, dyes, pigments and fillerssuch as calcium carbonate as is well known in the art. These plastisols,however, do not ordinarily exhibit any significant adhesive propertieswhich would make them useful for typical adhesive uses.

In order that the plastisol is provided with suitable adhesiveproperties which will cure rapidly and preferably at reducedtemperatures in the vicinity of 290 F. to 320 F., small quantities of adior polyhydric phenol having 3 or 4 hydroxyl groups attached to thebenzene ring or an aminophenol is added to the plastisol together with asubstance which is substantially non-reactive toward these aromaitchydroxy compounds at room temperatures but which at elevatedtemperatures will generate an aldehyde to produce reactive conditionsleading to the formation of a phenol-aldehyde-type condensation productwhich imparts to thevinyl plastisol excellent adhesion properties.

A preferred embodiment of the vinyl plastisol adhesive of this inventionconsists of a plastisol-grade polyvinyl chloride thoroughly dispersed ina dioctyl phthalate plasticizer in proportions of about 100 parts of theplasticizer by weight to 100 parts of the resin. The proportion of theplasticizer-to" resin may range from about parts of;

the plasticizer per 100 parts of the resin to about 125 parts of theplasticizer to 100 parts of the resin depending on the viscosity of theplasticizer and the particular character of the resin used as is wellknown in the art. The resin portion may include copolymers of polyvinylchloride and similar polymers such as polyvinyl acetate. In order thatthe plastisol is provided with suitable adhesive properties which willcure in the temperature range'of about 290 F. to 320 -F., about 1% byweight ofresorcinol together with about 2% by weight ofhexamethylenetetramine are added to the vinyl plastisol in a'substantially unreacted condition. These ingredients which are solids atroom temperature may be ground to a fine powder and'mixed with the vinylresin powder before mixing withthe plasticizer, 'or they may be wettedwith a little plasticizer and mixed with the plastisol. Satisfactoryadhesion and cure in the aforementioned temperature range is obtainedwith a variance of the resorcinol of between about 0.3% and 3% by weightand a variance in the hexamethylenetetrarnin e of about 0.1% to 6% byweight. The I upper limits of 3% and 6% respectively for the resorcinolsorcinol and hexamethylenetetramine above the limits of 3% and 6% isgreater than that required below these limits. Amounts of resorcinol andhexamethylenetetramine up to 10% and 15% respectively may be used.However, beyond this point the adhesive on curing loses the desireddegree of flexibility; These ingredients are, of

- course, thoroughly mixed to form a homogeneous mixture.

Various ingredients commonly included in plastisols such as stabilizersin the form of barium-cadmium compounds and dibasic lead phosphate,fillers such as calcium carbonate and dyes and pigments may be added tothe plastisol.

It has been found that various dihydroxy, trihydroxy and tetrahydroxyphenols and m-aminophenol may be substituted in place of the resorcinolin similar proportions with similar results. Other dihydroxy phenolsfound satisfactory include catechol and hydroquinone. Trihydroxy phenolsfound suitable include phloroglucinol, pyrogallol andhydroxyhydroquinone. Tetrahydroxy benzene and 2,2',4,4tetrahydroxybenzophenone have also been found suitable.

Other aldehyde-generating substances which may be used in place of thehexamethylenetetramine in similar proportions include paraformaldehyde,aldehyde ammonia, trioxane plus a catalyst such as aluminum chloride,zinc chloride and boron trifluoride monoethylamine. The aldehyde ammoniaon being heated produces acetaldehyde and reacts with the diorpolyhydric phenol or aminoinch. The ends of the paper elements 10 arethen immersed in the plastisol layers, care being taken so that theplates 14 are parallel to each other and each end of the paper elementis enveloped in the vinyl plastisol adhesive. The assembly is thenplaced in an oven maintained between about 290 F. and 320 F. for a timesufficient to cure the paper impregnant to about 83% to 92% of itscompletely cured state and to cause a fusion of the plastisol and a cureof the polyhydroxy benzene-aldehydegenerating compound components.During the heating process the formaldehyde-generating componentsgenerate.

formaldehyde or the equivalent thereof to produce reactive conditionsfavorable to. the production of adhesive thermosetting condensationproducts. The bond between the end plates 14 and the paper element 10 isstronger than the paper conventionally used in filter applications. Asis understood in the art, the filter paper impregnant is cured to'about83% to 92% of completion sinceabove this percentage of cure the papertends to become excessively brittle while below this range, the uncuredportions of the impregnant tend to be dissolved out by the hydrocarbonbeing filtered.

The time during which the paper element is kept within the oven in thetemperature range of 290 F. to 320 F. will vary considerably with theparticular characteristics of each oven. However, in accordance withthis invention, the time of cureis similar to that necessary to achievea'cure of about 83% to'92% of the impregnant as well as a fusion of theplastisol and the formation and cure of the polyhydroxyoraminophenol-aldehyde coma mixed withthe plastisol do not reduce itsshelf-life. The

material develops adhesive properties only after being heated to anelevated tempertaure so as to cause the aldehyde-generating substance todecompose and produce the free aldehyde and an environment favorable tothe reaction of the aldehyde and the polyhydric or aminophenol.

The aldehyde-generating substance is selected to generate an aldehyde atelevated temperatures so that no significant reaction takes placebetween the phenolic compound and the aldehyde-generatingcompound atroom or shop temperatures. In this context, the term elevatedtemperature is intended to refer to a temperature substantially aboveroom or shop temperatures, for example,

temperatures in excess of about 150 F.

Although the invention has been described in terms of certainembodiments, it is to be understood that variations may be employed andthe invention is notlimited thereby except as defined in the followingclaims.

We claim:

1. In a process for making filter elements the steps comprising forminga paper tube having ends and bonding rigid end plates to said ends bymeans of an adhesivecomposition comprising a vinyl plastisol includingsmall amounts of a phenol having from 2 to 4 hydroxyl groups and acompound capable of generating an aldehyde at elevated temperaturesreactive with said phenol, said amounts being sufficient to impartadhesive properties to said plastisol.

2. A process for making filter elements comprising the steps of forminga paper tube having ends, placing an end plate adjacent one of saidends, applying a layer of adhesive between said one end and said endplate, said adhesive comprising a vinyl plastisol including a phenolhaving from 2 to 4 hydroxyl groups and a compound capable of generatingan aldehyde in excess of about 290 F. reactive with said phenol, andheating the assembly at a temperature of about 290 F. to 320 F. for atime sufficient to effect a fusion of said vinyl plastisol and areaction and cure of said phenol and said aldehyde, to effect a bondbetween said one end and said end plate.

3. A process for making a filter element comprising the steps ofimpregnating filter paper with a phenolic resin capable of curing in atemperature range of about 290 F. to'320 F., forming said paper into atubular configuraends, applying an adhesive layer between said end plateand said one end, and subjecting the assembly to heat at a temperatureof from about 290 F. to 320 F. for

a time suflicient to cure said adhesive and said resin to a degree ofabout 83% to 92%, said adhesive comprising a vinyl plastisol includingat least 0.3% by weight of a phenol having 2 to 4 hydroxyl groups and acompound capable of generating an aldehyde at elevated temperatures.

4. A process for making a filter element comprising the steps ofimpregnating filter paper with a phenolic resin capable of curing in atemperature range of about 290 F. to 320 F., forming said paper into atubular configuration having ends, placing an end plate adjacent one ofsaid endaap plying an adhesive layer between said end plate and said oneend, subjecting the assembly to heat at a temperature from about 290 F.to 320 F. for a time sufficient to cure said adhesive and said resin toa degree or about 83% to 92% of completion, said adhesive comprising avinyl plastisol including about 0.3% to 3% by weight of a phenol having2 to 4 hydroxyl groups and about 0.1% to 6% by weight ofhexamethylenetetramine.

5. A process for making a filter element comprising the steps ofimpregnating filter. paper with a phenolic resin capable of curing in atemperature range of about 290 F. to 320 F., forming said paper into atubular configuration having ends, placing an end plate adjacent one endof said paper element, applying an adhesive layer between said end plateand said one end, subjecting the assembly to heat at a temperature fromabout 290 F. to 320 F. for a time sufiicient to cure said adhesive andsaid resin to a degree of about 83% to 92% of completion, said adhesivecomprising a vinyl plastisol including at least 0.3 by weight ofresorcinol and at least 0.1% by weight of a compound capable ofgeneratingan aldehyde at elevated temperatures.

6. A process for making a filter element comprising the steps ofimpregnating filter paper with a phenolic resin capable of curing in atemperature range of about 290 F. to 320 F., forming said paper into atubular configuration having ends, placing an end plate adjacent one endof said paper element, applying an adhesive layer between said end plateand said one end, and subjecting the assembly to heat at a temperatureof from about 290 F. to 320 F. for a time sufiicient to cure saidadhesive and said resin to a degree of about 83% to 92%, said adhesivecomprising a vinyl plastisol including at least 0.3% by weight ofaminophenol and a compound capable of generating an aldehyde at elevatedtemperatures.

References Cited in the file of this patent UNITED STATES PATENTS2,542,048 Nagel Feb. 20, 1951 2,739,916 Parker Mar. 27, 1956 2,749,265Fricke et a1. June5, 1956 2,951,769 McKnight Sept.6, 1960 FOREIGNPATENTS 120,558 Australia Nov. 5, 1945

1. IN A PROCESS FOR MAKING FILTER ELEMENTS THE STEPS COMPRISING FORMINGA PAPER TUBE HAVING ENDS AND BONDING RIGID END PLATES TO SAID ENDS BYMEANS OF AN ADHESIVE COMPOSITION COMPRISING A VINYL PLASTISOL INCLUDINGSMALL AMOUNTS OF A PHENOL HAVING FROM 2 TO 4 HYDROXYL GROUPS AND ACOMPOUND CAPABLE OF GENERATING AN ALDEHYDE AT ELEVATED TEMPERATURESREACTIVE WITH SAID PHENOL, SAID AMOUNTS BEING SUFFICIENT TO IMPARTADHESIVE PROPERTIES TO SAID PLASTISOL.